Hey, don't let science cloud you minds boys.

However I do have some scepsis about Hakan doing 18.5 knots sailing downwind in 6-12 knots winds (average 9 knots?); spi or no spi.

Even if he is sailing at 140 degrees of the wind (a gybe angle of only 40 and a VMG factor of 77%) ; his sails are then operating at an angle of attack of only 28 degrees with an apparent wind velocity of only 12.5 knots. Such angles of attack are typically only found on upwind legs and I've never been able to fly the spi there. It will collapse at angles of attack of less then 40 degrees.

My experience is that not more then 150% of the wind velocity is possible under spinnaker when sailing downwind and in perfect conditions.

Wouter